The statements in this section merely provide background information related to the present disclosure and may or may not constitute prior art.
A one way or overrunning clutch is an ingenious mechanical device typically associated with two co-axial or concentric components in a power or torque transmitting assembly or machine. The unique feature or capability of a one way clutch is its action in response to opposite relative rotational motion between its two or more components. When, in one direction, a first component attempts to drive or rotate faster than a second component, a one way clutch releases, allows the faster first component to freewheel and transfers essentially no torque. In the opposite rotational direction, unless the second component is rotating faster than the first component, the one way clutch locks and transfers or reacts torque from the first component to the second component up to the torque carrying limit of the clutch. When the second component is the torque input or drive member, the one way clutch operates in the reverse manner.
Because of their unique function and capability, one way or overrunning clutches have found broad application in mechanical power transfer devices such as multiple speed transmissions utilized in motor vehicles. For example, a one way clutch may restrain, i.e., ground, a transmission component in reverse and allow it to freely rotate in a forward gear or the one way clutch may restrain a component in one speed range or gear ratio and release it in another speed range or gear ratio.
There are several common one way clutch configurations. A sprag one way clutch utilizes a pair of concentric rings that nominally function as the input and output members and a plurality of oblique bars or sprags disposed between the rings. In one direction of relative rotation, the sprags are urged to tilt or relax such that one ring readily rotates (freewheels) relative to the other. With the opposite direction of relative rotation, the sprags move toward a more radial position and lock the inner and outer rings together. Ball ramp one way clutches utilize a plurality of ball bearings between the rings and corresponding ramps on the inner surface of one of the rings. Again, in one direction of relative rotation, the balls are urged to the bottom of the ramps and the rings freewheel. Relative rotation in the opposite direction causes the ball bearings to ride up the ramps, engage the other ring and lock them together.
While these and other, similar one way clutch configurations function well when the device has a relatively small diameter such as would be utilized with a shaft, engineering complications arise as the diameter of the controlled mechanical element becomes large. For example, in a transmission having a plurality of planetary gear assemblies, it may be unavoidable that a one way clutch must be installed about the ring gear of a planetary gear assembly. A one way clutch so mounted will require a large number of sprags or ball bearings in addition to much larger races. The device will thus weigh significantly more than a smaller, shaft mounted clutch.